The present invention relates to a refractory plate for use as a stationary and/or as a movable closure plate in a sliding closure unit, either of the linear movable or rotary movable type, for controlling the discharge of molten metal from a metallurgical vessel. The present invention further relates to a sliding closure unit employing such refractory plate or plates. The invention even further relates to a method of use of such plate or plates for increasing the useful life thereof in the operation of such a sliding closure unit.
Refractory plates are known for use as a stationary closure plate fixed in relation to a metallurgical vessel and as a movable closure plate in sliding contact with the stationary closure plate and slidable with respect thereto. The stationary and movable plates each have therethrough at least one discharge opening. The movable plate is slidable with respect to the stationary plate between an open position with the discharge openings in alignment, thereby discharging melten melt from the vessel, and a closed position with the discharge opening of each plate being blocked by an abutting sliding surface of the other plate, thereby interrupting discharge of the molten metal. Thus, in the closed position of the unit, the discharge opening in the stationary plate is covered by the respective sliding surface of the movable plate, i.e. the so-called working surface thereof on which rests the molten metal. During use of the unit, the abutting sliding surfaces of the two plates in the areas of the discharge openings thereof become damaged due to corrosion and erosion by the molten metal. This causes the discharge openings to be enlarged to an undesirable degree during continued use of the unit. As a result, the unit does not provide the necessary tightness and sealing, and the stationary and movable plates can be used for only a few discharge operations, after which they must be discarded.
Since the closure plates are formed primarily of high quality ceramic refractory material, attempts have been made in the past to prolong the useful life of the closure plates by rotating them or by turning them over so that opposite surfaces of the plates are placed in sliding abutting contact. However, this employs the same discharge openings which already are erosion damaged and thereby considerably weakened. The use of the plates in this reversed position therefore is significantly less than the first use of the plates before reversal. With regard to rotary sliding closure units, it has been attempted to rotate the plates to put into use entirely new discharge openings. However, this solution requires that plural discharge openings in the plates be spaced by a considerable distance to ensure the necessary working surfaces between adjacent openings. This has resulted in arrangements of rotary units having plates with only two or three discharge openings without unduly increasing the size of the units.